面向 Java 开发人员的 db4o 指南: db4o 中的数据库重构

                package com.tedneward.model;

public class Person
{
       
    public Person()
    { }
    public Person(String firstName, String lastName, int age)
    {
       
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    public String getFirstName() { return firstName; }
    public void setFirstName(String value) { firstName = value; }

    public String getLastName() { return lastName; }
    public void setLastName(String value) { lastName = value; }

    public int getAge() { return age; }
    public void setAge(int value) { age = value; }

    public String toString()
    {
       
        return 
            "[Person: " +
            "firstName = " + firstName + " " +
            "lastName = " + lastName + " " +
            "age = " + age + 
            "]";
    }

    public boolean equals(Object rhs)
    {
       
        if (rhs == this)
            return true;

        if (!(rhs instanceof Person))
            return false;

        Person other = (Person)rhs;
        return (this.firstName.equals(other.firstName) &&
                this.lastName.equals(other.lastName) &&
                this.age == other.age);
    }

    private String firstName;
    private String lastName;
    private int age;
}

                import java.io.*;
import java.lang.reflect.*;
import com.db4o.*;
import com.tedneward.model.*;

// Version 1
public class BuildV1
{
       
    public static void main(String[] args)
        throws Exception
    {
       
        new File(".", "persons.data").delete();

        ObjectContainer db = null;
        try
        {
       
            db = Db4o.openFile("persons.data");

            Person brianG = new Person("Brian", "Goetz", 39);
            Person jason = new Person("Jason", "Hunter", 35);
            Person brianS = new Person("Brian", "Sletten", 38);
            Person david = new Person("David", "Geary", 55);
            Person glenn = new Person("Glenn", "Vanderberg", 40);
            Person neal = new Person("Neal", "Ford", 39);
            Person clinton = new Person("Clinton", "Begin", 19);

            db.set(brianG);
            db.set(jason);
            db.set(brianS);
            db.set(david);
            db.set(glenn);
            db.set(neal);
            db.set(clinton);

            db.commit();

            // Find all the Brians
            ObjectSet brians = db.get(new Person("Brian", null, 0));
            while (brians.hasNext())
                System.out.println(brians.next());            
        }
        finally
        {
       
            if (db != null)
                db.close(); 
        }
    }
}

                package com.tedneward.model;

public enum Mood
{
       
    HAPPY, CONTENT, BLAH, CRANKY, DEPRESSED, PSYCHOTIC, WRITING_AN_ARTICLE
}

                package com.tedneward.model;

// Person v2
public class Person
{
       
    // ... as before, with appropriate modifications to public constructor and
    // toString() method

    public Mood getMood() { return mood; }
    public void setMood(Mood value) { mood = value; }

    private Mood mood;
}

                import com.db4o.*;
import com.tedneward.model.*;

// Version 2
public class ReadV2
{
       
    public static void main(String[] args)
        throws Exception
    {
       
// Note the absence of the File.delete() call

        ObjectContainer db = null;
        try
        {
       
            db = Db4o.openFile("persons.data");

            // Find all the Brians
            ObjectSet brians = db.get(new Person("Brian", null, 0, null));
            while (brians.hasNext())
                System.out.println(brians.next());            
        }
        finally
        {
       
            if (db != null)
                db.close(); 
        }
    }
}

                
[Person: firstName = Brian lastName = Sletten age = 38 mood = null]
[Person: firstName = Brian lastName = Goetz age = 39 mood = null]

                import com.db4o.*;
import com.tedneward.model.*;

// Version 2
public class BuildV2
{
       
    public static void main(String[] args)
        throws Exception
    {
       
        ObjectContainer db = null;
        try
        {
       
            db = Db4o.openFile("persons.data");

            // Find all the Persons, and give them moods
            ObjectSet people = db.get(Person.class);
            while (people.hasNext())
            {
       
                Person person = (Person)people.next();

                System.out.print("Setting " + person.getFirstName() + "'s mood ");
                int moodVal = (int)(Math.random() * Mood.values().length);
                person.setMood(Mood.values()[moodVal]);
                System.out.println("to " + person.getMood());
                db.set(person);
            }

            db.commit();            
        }
        finally
        {
       
            if (db != null)
                db.close(); 
        }
    }
}

                Setting Brian's mood to BLAH
Setting David's mood to WRITING_AN_ARTICLE
Setting Brian's mood to CONTENT
Setting Jason's mood to PSYCHOTIC
Setting Glenn's mood to BLAH
Setting Neal's mood to HAPPY
Setting Clinton's mood to DEPRESSED

                
[Person: firstName = Brian lastName = Sletten age = 38]
[Person: firstName = Brian lastName = Goetz age = 39]

                import com.db4o.*;
import com.db4o.config.*;

// ...

Db4o.configure().objectClass("com.tedneward.model.Person")
    .rename("com.tedneward.persons.model.Individual");

                import com.db4o.config.*;

// ...

TypeAlias fromPersonToIndividual = 
    new TypeAlias("com.tedneward.model.Person", "com.tedneward.persons.model.Individual");
Db4o.configure().addAlias(fromPersonToIndividual);